From the perspective of the radio network side, there are two states, i.e., the RRC_connected state and the RRC_idle state, of a terminal in a Long Term Evolution (LTE) system; and in a Universal Mobile Telecommunication System (UMTS) there are five states of a terminal, i.e., CELL_DCH, CELL_FACH, CELL_PCH/URA_PCH, and Idle states, where CELL_DCH, CELL_FACH, and CELL_PCH/URA_PCH belongs to the RRC_connected state, and only the terminal in the RRC_connected state can transmit uplink data. Once the terminal completes the transmission of data, the network side releases the RRC connection of the terminal in a Radio Resource Control (RRC) Connection Release message upon detecting that the terminal has no data transmitted for a long period of time, so that the terminal enters the RRC_idle state.
The terminal in the idle state primarily operates to detect paging by the network side. In order to save power, the terminal generally detects paging in a Discontinuous Reception (DRX) mode in which the terminal is in a receiving state only for a short period of time in each cycle and in a non-receiving state in the remaining period of time in the cycle. In the UMTS system, the length of time of a DRX cycle configured at the network side at present is at most 29 radio frames length (i.e. 5120 ms), that is, from the perspective of DRX in the UMTS system, the terminal enables a receiver at most once every 5120 ms to receive a paging instruction message, and possibly a paging message, of the network side but disables the receiver in the remaining period of time. The longest DRX cycle configured at the network side at present in the LTE system is 2560 ms.
There are possibly two DRX lengths configured for the terminal in both the UMTS system and the LTE system: one is configured by a Radio Network Controller (RNC)/evolved Node B (eNB) in a System Information Block (SIB) message and can be referred to a default DRX, which is applicable to all of terminals camping on the cell. The other is negotiated by a Core Network (CN) entity and the terminal in a Non-Access Stratum (NAS) procedure and can be referred to a User Equipment (UE) specific DRX, which is only applicable to a single terminal. The latter one is unknown to the RNC/eNB in the negotiation procedure.
The paging message is firstly transmitted by the core network to the access network, i.e., the RNC (UMTS)/eNB (LTE), and in the LTE system, transmitted by a core network entity, i.e., a Mobility Management Entity (MME), via an S1 interface as illustrated in FIG. 1; and in the UMTS system via an Iu interface, as illustrated in FIG. 2. If the paging message carries the UE specific DRX configuration, then in the UMTS system, the RNC transmits the paging message via the air interface using a DRX parameter configured in the paging message; or in the LTE system, the eNB compares the DRX parameter in the DRX configuration with a DRX parameter configured in a system message and transmits the paging message using the shorter one of the DRX cycles.
As specified in the 36.304 protocol in the LTE system, and the 25.304 protocol in the UMTS system, it is determined that there is a direct relationship between the calculation of the occasion at which the UE receives paging and a System Frame Number (SFN) and an International Mobile Subscriber identity (IMSI). Taking the UMTS system as an example, it is specified in the 25.304 protocol that Paging Occasion={(IMSI div K) mod (DRX cycle length div PBP)}*PBP+n*DRX cycle length+Frame Offset, n=0, 1, 2, . . . , as long as the SFN is below its maximum value, where K represents a coefficient of the DRX cycle length, the DRX cycle length represents the length of the DRX cycle, PBP represents the cycle of a paging block, the Frame Offset represents a frame offset, and n ranges from 0 to the maximum value of the SFN. Apparently the value of n is limited to the maximum value of the SFN, so the paging cycle in the UMTS system is also limited to the maximum value of the SNF. This will also apply to the LTE system.
Moreover time information is exchanged as defined below in the existing protocol: in the LTE system, detailed time information can be provided in the SIB 16 in the 36.331 protocol; and in the UMTS system, time information can be available at present from Multimedia Broadcast Multicast Service (MBMS) information of Least-Cost Route (LCR) Time Division Duplex (TDD), and this network standard time is only used for an MBMS service but has not been applicable to other functions. In the LTE system, this time can be provided for use by a higher layer in a Code Division Multiple Access 2000 (CDMA 2000) system and can also be applicable to positioning, Minimization of Drive Test (MDT) and an MBMS.
Machine-Type Communication (MTC), which is a new communication concept, is intended to integrate a number of different types of communication technologies together, e.g., machine-to-machine communication, machine controlled communication, human-to-machine interactive communication, mobile Internet communication, etc., to thereby develop social production and life styles. As expected, human-to-human communication services will account for only one third of the terminal markets in the future, whereas a larger amount of communication will emerge as MTC communication services. Sometimes MTC communication is also referred to as Machine-to-Machine (M2M) communication or the Internet of Things.
An important issue of power saving needs to be considered in the MTC communication scenario. In some scenarios, the lifetime of an MTC device is determined directly by the lifetime of a battery, for example, an MTC device for tracking an animal or an MTC device for hydrologic supervision, for both of which it is nearly impossible to replace batteries, so the MTC device is required to consume an extremely low amount of power.
The longest existing paging cycle will not exceed the maximum length of the SFN, but in fact, even the longest DRX cycle may result in too frequency operations, particularly for an MTC terminal which only communicates occasionally with the network, so it is not good for the terminal saving power.